n = int(input())
a=[int(i) for i in input().split(" ")]

i=0
j=0
while i+3<=n:
    b=a[i:i+3]
    c=sorted(a[i:i+3])

    if (c[1]==b[0] or c[1]==b[-1]) and b[0]!=b[1] and b[1]!=b[2] and b[0]!=b[2]:
        j+=1
    
    else:
        j+=0


    i+=1

print(j)